The Weird Ways People React to Driving Bans

As cities try to control their air pollution with driving bans, research finds citizens react by buying more cars, watching more television, and, sometimes, by driving less and contributing to lower pollution in their towns.

This week, the city temporarily enacted a policy that's perhaps most commonly associated with smoggy Beijing, mandating that only cars with license plates ending in an odd number be allowed to drive on Monday, while only even-numbered plates be allowed to hit the road on Tuesday. Romans who don't comply will be hit with fines.

It's not just Beijing and Rome. Cities ranging from São Paulo to Amsterdam have used driving bans—often based on license-plate numbers—to try to reduce pollution and traffic. Those are worthwhile goals: Besides inconveniences like grounded flights (because of low visibility), air pollution causes health problems that kill millions of people around the world every year.

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Driving bans seem to work better when they last longer—all day instead of part of a day, for perhaps several days a week—and cover a larger geographic area.

But do driving bans actually work to reduce air pollution in cities? The research bears mixed results. Bans' effectiveness probably depends on how severe and widespread they really are. Meanwhile, researchers have uncovered some funny reactions to the bans, from increased procrastination to an uptick in car purchases.

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One study found that, after Mexico City enacted a law in 1989 prevented car-owners from driving one day per week (based on their cars' license-plate numbers), city residents actually bought more cars. Presumably, drivers were trying to secure a wider variety of license plate numbers that would in turn let them drive when they wanted to. Not surprisingly, air pollution measures didn't fall.

However, earlier this year, a new study of Beijing found both once-a-week and every-other-day bans indeed did reduce air pollution measures on the affected days. (Not all studies of Beijing have been entirely positive. A 2011 study found that one-day-a-week bans didn't alter air pollution in China's capital, but every-other-day bans did.) The more recent research also discovered another effect of the driving bans: Self-employed Beijingers watched more television on days their cars were stalled, suggesting that they were following the rules and that the bans affected their productivity. Still, the health benefits of lesser pollution outweighed the cost of lazy freelancers, wrote the study's authors.

What's a city to do? Driving bans seem to work better when they last longer—all day instead of part of a day, for perhaps several days a week—and cover a larger geographic area, wrote the authors of the 2011 study. Otherwise, people will just do all their driving during the non-ban times. Meanwhile, the authors of the 2015 study suggest cities discourage driving in other ways, such as raising vehicle licensing fees and collecting tolls based on congestion. A few cities have tried those methods, and indeed sometimes they do work.

While, we're at it, how about the effectiveness of a ban on wood-fired pizza ovens, enacted recently by the Italian city of San Vitaliano? Actually, cities have tried their own local versions of that too. A ban on coal sales in Dublin reduced deaths from heart and respiratory diseases, one study found, while another study shows that a program encouraging wood stove owners in Libby, Montana, to retrofit their stoves or replace them with propane, oil, and gas units left a marked improvement on the town's air.

It seems cities have tried everything to combat air pollution, and some of these strategies can, in fact, work.

Francie Diep is a staff writer at Pacific Standard, where she specializes in health and drug policy and the intersections of culture and science. Previously, she covered science, health, and science policy for Scientific American, Popular Science, and Smithsonian.